著者

Yuhji Kuroda Miho Toryu Hiroaki Naoe

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.47-52, 2022 (Released:2022-03-18)

参考文献数

21

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This study examined the influence of stratospheric variability on the polar winter tropospheric climate. The winter-mean tropospheric condition can be well represented by a winter-mean stratospheric index (the Polar-night Jet Oscillation (PJO) index) defined from profiles of monthly polar temperature anomalies. In winters with a positive (negative) index, the winter-mean surface pressure anomaly tends to acquire a positive (negative) pattern resembling the Arctic Oscillation (AO). This tropospheric condition tends to become a persistent polarity of the AO index throughout the winter. This tendency is also found when the PJO index for each month is used. Although the PJO index in January shows the best results, those in early winter can be used as predictors for the entire winter troposphere. Use of the PJO index for the stratospheric effect on winter troposphere is compared with that associated with the occurrence of the major stratospheric sudden warmings. The origin of the decadal variability of the index is also discussed.

著者

Yuhji Kuroda Miho Toryu Hiroaki Naoe

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2022-008, (Released:2022-01-27)

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This study examined the influence of stratospheric variability on the polar winter tropospheric climate. The winter-mean tropospheric condition can be well represented by a winter-mean stratospheric index (the Polar-night Jet Oscillation (PJO) index) defined from profiles of monthly polar temperature anomalies. In winters with a positive (negative) index, the winter-mean surface pressure anomaly tends to acquire a positive (negative) pattern resembling the Arctic Oscillation (AO). This tropospheric condition tends to become a persistent polarity of the AO index throughout the winter. This tendency is also found when the PJO index for each month is used. Although the PJO index in January shows the best results, those in early winter can be used as predictors for the entire winter troposphere. Use of the PJO index for the stratospheric effect on winter troposphere is compared with that associated with the occurrence of the major stratospheric sudden warmings. The origin of the decadal variability of the index is also discussed.

著者

Yuhji KURODA Kunihiko KODERA

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.3, pp.171-180, 2017 (Released:2017-04-28)

参考文献数

14

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This paper proposes a new simple method of multivariable maximum covariance analysis (MMCA) for extracting common variability from multiple (more than two) datasets that expands the singular value decomposition analysis method. The method is based on iteration of a recurrence equation derived by a dual relationship between pattern vectors and time coefficients. Two approaches of the method are proposed, one using the extreme of a summation of covariances (sum MMCA) and the other using the product of covariances (product MMCA). Both approaches are demonstrated by successfully extracting the variability related to the Arctic Oscillation from three monthly-mean meteorological datasets. The method is useful because it is easily programmed and is computationally inexpensive. The method can be applied to an arbitrary number of datasets, although a complete set of the product MMCA method cannot be applied to an even number of datasets.

著者

Kunihiko KODERA Nawo EGUCHI Jae N. LEE Yuhji KURODA Seiji YUKIMOTO

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.89, no.3, pp.283-290, 2011-06-25 (Released:2011-06-30)

参考文献数

24

被引用文献数

7 18

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In mid-January 2009, sudden changes in circulation occurred in the tropical troposphere and stratosphere. Convective activity situated over the equatorial Maritime Continent showed an abrupt weakening, whereas that over the South American to African sectors became stronger. Changes also occurred in the latitudinal structure; convective activity in the Northern Hemisphere became weaker, whereas that in the Southern Hemisphere became stronger. The change in convective activity took place in association with a change in tropical circulation, from east–west to north–south type (i.e., from Walker- to Hadley-type circulation). Almost simultaneously with these events in the troposphere, a change in meridional circulation occurred in the stratosphere during a record-breaking stratospheric sudden warming event in January 2009. Stratospheric tropical temperature showed a decrease in response to a strengthening of the hemispherical meridional circulation. In the present study, we show how the stratospheric and tropospheric circulation changes are dynamically coupled.

著者

Yuhji KURODA

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.85, no.6, pp.889-898, 2007 (Released:2008-03-20)

参考文献数

22

被引用文献数

8 15

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The effect of the Quasi-Biennial Oscillation (QBO) and the El Niño Southern Oscillation (ENSO) on the 11-year solar cycle modulation of the winter-mean North Atlantic Oscillation (NAO) is examined through analysis of observational data from 1958 to 2000. It is found that the solar cycle modulation of the NAO is more strongly enhanced in the westerly phase of the 50-hPa QBO wind and the cold phase of ENSO, although separation of these effects is statistically difficult. On these phases, the signal of the winter-mean NAO extends more to the upper stratosphere and summer-AO reappears more strongly in high solar years, whereas the signal is weaker throughout in low solar years.

著者

Yuhji KURODA Kunihiko KODERA

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.80, no.4B, pp.973-984, 2002 (Released:2002-10-10)

参考文献数

31

被引用文献数

32 59 42

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Effect of the modulation of the Polar-night jet oscillation (PJO) in winter time by the 11-year solar cycle is examined by the observational data from 1979 to 1999. It is found that zonal wind and the E-P flux anomalies appear commonly in the subtropical upper stratosphere in early winter of both the Northern and Southern Hemispheres as a response to meridional UV heating contrast. These zonal wind anomalies are found to propagate poleward and downward with development as a seasonal march in both hemispheres. Although the length of the record is limited, it is suggested from the available data that the signal due to solar activity appears as the time evolution of the PJO triggered by solar forcing at early winter in both hemispheres. Differences in the signals between the Northern and Southern Hemispheres during late winter are explained in terms of the different characteristics of the PJO in each hemisphere. A significant temperature signal is also found to appear in the Southern Hemisphere in late winter under a solar maximum condition.